1. Field of the Invention
The present invention relates to an image sensor to be used for image pickup apparatuses such as digital cameras, and particularly to an image sensor suitable for photoelectric conversion of light fluxes from plural areas of an exit pupil of an image capturing optical system.
2. Description of the Related Art
An image pickup apparatus using such an image sensor is disclosed in U.S. Pat. No. 4,410,804. The disclosed image pickup apparatus uses a two-dimensional image sensor that includes plural pixels each being constituted by one microlens and plural separated photoelectric conversion portions. The separated photoelectric conversion portions receive, through the one microlens, light fluxes from mutually different areas of an exit pupil of an image capturing optical system (the mutually different areas of the exit pupil are hereinafter referred to as “partial pupil areas”), that is, perform pupil division. The disclosed image pickup apparatus can produce, by using electric signals obtained through photoelectric conversion by the photoelectric conversion portions, parallax images corresponding to the partial pupil areas.
The produced parallax images are equivalent to Light Field (LF) data that is information on a spatial distribution and an angular distribution of light intensity. “Stanford Tech Report CTSR 2005-02, 1 (2005)” discloses a refocus technology that reconstructs, by using acquired LF data, an image at a virtual imaging surface different from an image sensor surface to produce a refocus image corresponding to an in-focus position different from that in an original captured image.
Moreover, Japanese Patent Laid-Open No. 2001-083407 discloses an image pickup apparatus that produces a captured image by adding electric signals from all separated photoelectric conversion portions in each of pixels in an image sensor.
Each pixel of such an image sensor includes a separating zone formed among the separated photoelectric conversion portions to separate them from one another. However, the separating zone often has a lower photo sensitivity than those of the photoelectric conversion portions. Such a separating zone forms a low sensitivity zone corresponding to a shape of the separating zone (in other words, a shape of the separated photoelectric conversion portions) in a pupil intensity distribution (in other words, an incident angle distribution of a light-receiving ratio) of each pixel, which may cause unnatural blur in the captured image.